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Atmospheric Hydrogen Mixing Ratios from the 
NOAA GMD Carbon Cycle Cooperative Global Air
Sampling Network, 1988-2005  

Version: 2006-11-27.1229
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CONTENTS

1.       Data source and contacts
2.       Use of data
3.       Reciprocity 
4.       Warnings
5.       Update notes
6.       Introduction
7.       DATA - General Comments
7.1      DATA - Sampling Locations
7.2      DATA - File Name Description
7.3      DATA - Event
7.4      DATA - QC Flags
7.5      DATA - Monthly Averages
8.       Data retrieval
9.       References

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1. DATA SOURCE AND CONTACTS

National Oceanic and Atmospheric Administration (NOAA)
Earth System Research Laboratory (ESRL)
Global Monitoring Division (GMD)
Carbon Cycle Greenhouse Gases (CCGG)

Correspondence concerning these data should be directed to:

Paul C. Novelli 
NOAA ESRL Global Monitoring Division
325 Broadway, GMD-1
Boulder, CO  80305
U.S.A.

Telephone: 303 497-6974
Electronic Mail: Paul.C.Novelli@noaa.gov

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2. USE OF DATA

These data are made freely available to the public and the
scientific community in the belief that their wide dissemination
will lead to greater understanding and new scientific insights.
The availability of these data does not constitute publication
of the data.  NOAA relies on the ethics and integrity of the user to
assure that GMD receives fair credit for their work.  If the data
are obtained for potential use in a publication or presentation,
GMD should be informed at the outset of the nature of this work.
If the GMD data are essential to the work, or if an important
result or conclusion depends on the GMD data, co-authorship may
be appropriate.  This should be discussed at an early stage in
the work.  Manuscripts using the GMD data should be sent to GMD
for review before they are submitted for publication so we can
insure that the quality and limitations of the data are accurately
represented.

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3. RECIPROCITY

Use of these data implies an agreement to reciprocate.
Laboratories making similar measurements agree to make their
own data available to the general public and to the scientific
community in an equally complete and easily accessible form.
Modelers are encouraged to make available to the community,
upon request, their own tools used in the interpretation
of the GMD data, namely well documented model code, transport
fields, and additional information necessary for other
scientists to repeat the work and to run modified versions.
Model availability includes collaborative support for new
users of the models.

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4. WARNINGS

Every effort is made to produce the most accurate and precise
measurements possible.  However, we reserve the right to make
corrections to the data based on recalibration of standard gases
or for other reasons deemed scientifically justified.

We are not responsible for results and conclusions based on use
of these data without regard to this warning.


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5. UPDATE NOTES


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6. INTRODUCTION

Individual site files provide H2 mixing ratios in parts 
per billion (ppb) (ppb = 1 part in 10^-9 by mole 
fraction = nmole/mole) based on measurements from the NOAA 
CMDL Carbon Cycle Cooperative Global Air Sampling Network. 
In this directory, data are provided through June 30, 1998 
for stations from which the first sample was collected before 
January 1995. Table 1, accessed below, lists the flask network 
sampling location, the 3 letter codes used to identify these
sites, their latitude, longitude and altitude. 

Data from sites not provided in this directory may be available
from P. Novelli (CMDL).  All air samples were analyzed for H2 
at the NOAA CMDL laboratory in Boulder using gas chromatography 
with mercuric oxide reduction detection, with all measurements 
referenced to an internal H2 calibration scale (Novelli et al.,
1999). During 1988-1991, one flask of a sample pair was analyzed
for H2, and when there was suitable pressure remaining in the 
flask, two or more aliquots were measured. We have used the
difference in H2 mixing ratios between the aliquots as an indication
of the precision of the measurements. We used a single point
calibration as the response characteristics of the instrument
had been shown to be linear over a range of 480 to 600 ppb CO 
(Novelli et al., 1999).

In October 1991 we began analyzing a single aliquot from
both members of a flask pair (rather than 2 or more aliqouts
from a single flask). The principle reasons for the change were
to simplify flask handling procedures (The CMDL carbon monoxide
and methane projects also measure both flasks of a sample pair)
and to use pair agreement (the difference in mixing ratio between
the two flasks collected simultaneously) as an additional diagnostic
to use in evaluating the quality of the data. We believe that pair
agreement provides quality constraints on the results from collection
through analysis.  Novelli et al. (1999) provide a detailed description
of the history of H2 measurements at CMDL.

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7. DATA - GENERAL COMMENTS

Measurements are reported in units of 10^-9 mol H2 per mol 
of dry air (nmol/mol) or parts per billion (ppb)) relative 
to the NOAA CMDL H2 scale (Novelli et al., 1999).  Long-term 
measurement uncertainty is estimated to be 15 ppb (~3%).  The 
absolute accuracy of our H2 scale is unknown.  In 2004 a 
correction was applied to all measurements made between Dec 1998 
and Nov 2002 to account for drift in a working standard.  The 
drift rate was determined from multiple calibrations using 
other H2 standards that are believed stable.

The Pacific Ocean Cruise (POC, travelling between the US west coast
and New Zealand or Australia), Atlantic Ocean Cruise (AOC, US east
coast to South Africa), and Western Pacific Cruise (WPC, New Zealand
and Japan) data have been merged and grouped into 5 degree latitude 
bins.  For the South China Sea cruises (SCS) the data are grouped in 
3 degree latitude bins.

Sampling frequencies are approximately weekly for the fixed sites
and average one sample every 3 weeks per latitude zone for POC and
about one sample every week per latitude for SCS.

The air samples are collected by two general methods:  flushing and
then pressurizing glass flasks with a pump, or opening a stopcock on
an evacuated glass flask.  During each sampling event, a pair of
flasks is filled.

7.1 DATA - SAMPLING LOCATIONS

<A HREF='http://www.cmdl.noaa.gov/ccgg/iadv/ccggmdb_list_available.php?gas=h2&project=flask'>
Table of NOAA GMD cooperative air sampling sites.</A>

The table includes the three letter code used to identify each 
site; the site name; latitude, longitude, and altitude (meters 
above sea level) of the sampling location; the number of samples;
the first and last sample dates; and sampling status.

Note: Data for all species may not be available for all sites listed 
in the table.

To view near real-time data, manipulate and compare data, and create
custom graphs, please visit

<A HREF='http://www.cmdl.noaa.gov/ccgg/iadv/'>http://www.cmdl.noaa.gov/ccgg/iadv/</A>.

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7.2 DATA - FILE NAME DESCRIPTION

Encoded into each file name is the sampling location, platform, and
strategy; measurement laboratory; file content; and gas identifier.
All file names use the following naming scheme:

 1     2               3     4         5          6           7
[site][data grouping]_[lab#][strategy][platform]_[qualifier].[gas]

1. [Sampling site]
   (ex) brw_, poc_, car_, amt_

2. [Grouping of data within the file]

   Data may be grouped by date, latitude, longitude, altitude, etc.
   
   If data are grouped by date then identifier has yyyy[mm][dd] format.
   (ex) brw2005_, amt200403_, lef20050315_

   If the sampling platform is an aircraft then the identifier is a
   3-character numeric field with units of 10^2 meters (hm) above sea level.
   (ex) car040_, haa005_

   If the sampling platform is a ship then the identifier is a 3-character 
   alphanumeric field with units of degrees (00-90).  Bins in the northern 
   and southern hemispheres are denoted as n## and s## respectively.  The 
   equatorial bin is denoted as 000.
   (ex) pocs25_, poc000_, scsn03_

3. [Measurement laboratory]

   A two character numeric field identifies the measurement laboratory (01-99).
   NOAA GMD is lab number 01 (see http://www.cmdl.noaa.gov/ccgg/globalview/labs/).

4. [Sampling strategy]

   A single alphanumeric character (0-9,a-z,A-Z) indicates the sampling strategy.

   _??C               Semi-continuous
   _??D               Discrete

5. [Sampling platform]

   A single alphanumeric character (0-9,a-z,A-Z) indicates the sampling platform.

   _???0              Land
   _???1              Ship
   _???2              Aircraft
   _???3              Tower

6. [Qualifier]

   An alphanumeric string describes the type of data included in the file.

   _????_event        Data from every collection event
   _????_mm           Computed monthly mean values
   _????_hr           Computed hourly averages (semi-continuous data only)
   _????_day          Computed daily averages (semi-continuous data only)
   _????_all          All Data

7. [Gas]

   Identifies the trace gas species.

   _????_???.co2      Carbon dioxide
   _????_???.ch4      Methane
   _????_???.co2c13   d13C (co2)

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7.3 DATA - EVENT

The data files "ccg/h2/flask/event/" use the following naming
scheme (see Section 7.2):

     xxx[data grouping]_01D[platform]_event.h2

(ex) pocn30_01D1_event.h2 contains all event data from 
     POC samples collected from a moving ship and grouped at 
     30N +/- 2.5 degrees.

(ex) brw_01D0_event.h2 contains all event data from
     from BRW samples collected from a fixed position.

The data files contain multiple lines of header information
followed by one line for each atmospheric measurement.

Fields are defined as follows:

Field 1:    [SITE CODE] The three-character sampling location code (see above).

Field 2:    [YEAR] The sample collection date and time in UTC.
Field 3:    [MONTH]
Field 4:    [DAY]
Field 5:    [HOUR]
Field 6:    [MINUTE]

Field 7:    [FLASK ID] The sample container ID.

Field 8:    [METHOD] A single-character code that identifies the sample 
             collection method.  The codes are:

             P - Sample collected using a portable, battery
                 powered pumping unit.  Two flasks are
                 connected in series, flushed with air, and then
                 pressurized to 1.2 - 1.5 times ambient pressure.

             D - Similar to P but the air passes through a
                 condenser cooled to about 5 deg C to partially
	         dry the sample.

             G - Similar to D but with a gold-plated condenser.

             T - Evacuated flask filled by opening an O-ring sealed       
                 stopcock.

             S - Flasks filled at NOAA CMDL observatories by sampling
                 air from the in situ CO2 measurement air intake system.

             N - Before 1981, flasks filled using a hand-held
                 aspirator bulb. After 1981, flasks filled using a
                 pump different from those used in method P, D, or G.

             F - Five liter evacuated flasks filled by opening a
                 ground glass, greased stopcock.

Field 9:    [TRACE GAS NAME] Gas identifier (e.g., co2, co2c13).

Field 10:   [MEASURED VALUE] Dry air mole fraction or isotopic composition.  
             Missing values are denoted by -999.99[9].

Field 11:   [QC FLAG] A three-character field indicating the results of our 
             data rejection and selection process, described in section 7.4.

Field 12:   [INSTRUMENT] A 2-character code that identifies the instrument 
             used for the measurement.

Field 13:   [YEAR] The measurement date and time in LT.
Field 14:   [MONTH]
Field 15:   [DAY]
Field 16:   [HOUR]
Field 17:   [MINUTE]

Field 18:   [LATITUDE] The latitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the southern hemipshere).

Field 19:   [LONGITUDE] The longitude where the sample was collected, (negative (-)
             numbers indicate samples collected in the western hemisphere).

Field 20:   [ALTITUDE] The altitude where the sample was collected (masl).

Field 21:   [WIND SPEED] Wind Speed (m/s) as reported by the field operator
             during sample collection.  Please note: CCCG has no means by which
             to assess the reliability of these recorded observations.

Field 22:   [WIND DIRECTION] Wind Direction (degrees) as reported by the field 
             operator during sample collection.  Please note: CCGG has no means
             by which to assess the reliability of these recorded observations.

Field 23:   [EVENT NUMBER] A long integer that uniquely identifies the sampling
             event.

Fields in each line are delimited by whitespace.

(ex)

   KEY 2004 12 17 15 00 2185-99 D co2 400.170 -.. L3 2005 01 03 13 52 25.66 -80.20 3.00 4.6 90 193357

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7.4 QC FLAGS

NOAA GMD uses a 3-column quality control flag where each column
is defined as follows:

column 1    REJECTION flag.  An alphanumeric other
            than a period (.) in the FIRST column indicates
            a sample with obvious problems during collection
            or analysis.  This measurement should not be interpreted.

column 2    SELECTION flag.  An alphanumeric other than a
            period (.) in the SECOND column indicates a sample
            that is likely valid but does not meet selection
            criteria determined by the goals of a particular
            investigation.

column 3    COMMENT flag.  An alphanumeric other than a period (.) 
            in the THIRD column provides additional information 
            about the collection or analysis of the sample.

            WARNING: A "P" in the 3rd column of the QC flag indicates
            the measurement result is preliminary and has not yet been 
            carefully examined by the PI.  The "P" flag is removed once 
            the quality of the measurement has been determined.

If both the first and second column contain a period (e.g., "..." and "..I"),
the sample is RETAINED.

Since samples are collected in pairs, the pair
difference is calculated, and samples with a
pair difference greater than 15 ppb are flagged.
Retained and rejected flasks are flagged as follows.

(NOTE: If either the first or second of these characters 
is not a period, the sample has been rejected.)


              Flag     Description

Retained      ... 	good pair
                        (D <= 15 ppb)



Rejected      .X.     Not representative of background
                      conditions (> 3 sigma from a fitted
                      curve), may include unidentified
		      sampling/analysis problems.

              .N.     High/low mixing ratio thought
                      to not represent background 
                      condiitons. 

              P..     Poor flask pair agreement
                      (D > 15 ppb)

              Z..     Poor aliquot agreement
                      (D > 7.5 ppb)

              *..     off scale result, broken flask or
                      unacceptable analysis

              W..     Wrong flask type for H2

              S..     Sample was collected through the CO2
                      intake for the in situ analyzer

              ..I     Flask is one of the pair used in an
                      intercomparison with the cooperating
                      agency

The retained values comprise the data set that we feel best
represents the H2 distribution in the remote, well-mixed 
global troposphere.  It is possible, and even likely, that 
some values flagged as non-background conditions are valid 
measurements, but represent poorly mixed air parcels 
influenced by local anthropogenic sources or strong local 
biospheric sources or sinks.  Users of these data should be 
aware that data selection is a difficult but necessary aspect 
of the analysis and interpretation of atmospheric trace gas 
data sets, and the specific data selection scheme used may be 
determined by the goals of a of a particular investigation.

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7.5 DATA - MONTHLY AVERAGES

The data files "ccg/h2/flask/month/" use the following naming
scheme (see Section 7.2):

     xxx[data grouping]_01D[platform]_mm.h2

(ex) pocn30_01D1_mm.h2 contains computed monthly mean values
     from POC samples collected from a moving ship and grouped at 
     30N +/- 2.5 degrees.

(ex) brw_01D0_mm.h2 contains computed monthly mean values 
     from BRW samples collected from a fixed position.

Monthly means are produced for each site by first averaging all
valid measurement results in the event file with a unique sample
date and time.  Values are then extracted at weekly intervals from 
a smooth curve (Thoning et al., 1989) fitted to the averaged data 
and these weekly values are averaged for each month to give the 
monthly means recorded in the files.  Flagged data are excluded from the
curve fitting process.  Some sites are excluded from the monthly
mean directory because sparse data or a short record does not allow a
reasonable curve fit.  Also, if there are 3 or more consecutive months
without data, monthly means are not calculated for these months.

The data files contain multiple lines of header information 
followed by one line for each available month.

Fields are defined as follows:

Field 1:    [SITE CODE] The three-character sampling location code (see above).

Field 2:    [YEAR] The sample collection year and month.
Field 3:    [MONTH]

Field 4:    [MEAN VALUE] Computed monthly mean value

In these files a monthly mean value of -999.99 denotes months where there
are insufficient data to calculate a monthly mean.

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8. DATA RETRIEVAL

To transfer all files in a directory, it is more efficient to 
download the tar or zipped files.  

To transfer a tar file, use the following steps from the ftp prompt:

   1. ftp> binary                    ! set transfer mode to binary
   2. ftp> get filename.tar.Z        ! transfer the file
   3. ftp> bye                       ! leave ftp

   4. $ uncompress filename.tar.Z    ! uncompress your local copy
   5. $ tar xvf filename.tar         ! unpack the file

To transfer a zipped file, use the following steps from the ftp prompt:

   1. ftp> binary                    ! set transfer mode to binary
   2. ftp> get filename.zip          ! transfer the file
   3. ftp> bye                       ! leave ftp

   4. $ unzip filename.zip           ! uncompress your local copy

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9. REFERENCES

Lang, P.M., L.P. Steele, R.C. Martin, and K.A. Masarie, Atmospheric 
  methane data for the period 1983-1985 from the NOAA/GMCC global  
  cooperative  flask sampling network, NOAA Technical Memorandum ERL 
  CMDL-1, 1990a.

Lang, P.M., L.P. Steele, and R.C. Martin, Atmospheric methane data for 
  the period 1986-1988 from the NOAA/CMDL global cooperative flask  
  sampling network, NOAA Technical Memorandum ERL CMDL-2, 1990b.

Novelli, P.C., K.A. Masarie, and P.M. Lang, Molecular hydrogen in the 
  troposhere: Global distributions and budget,  J. Geophys Res., 104, 
  30,427-30,444, 1999.

Thoning, K.W., P.P. Tans, and W.D. Komhyr, 1989, Atmospheric carbon 
  dioxide at Mauna Loa Observatory 2. Analysis of the NOAA
  GMCC data, 1974-1985, J. Geophys. Res., 94, 8549-8565.

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